This invention relates to a two-layer enclosure for an electrical assembly, and more particularly to a two-layer enclosure construction for power supply units for cell phone battery chargers, laptop adapters, or the like that substantially reduces the cost of mass-producing electrical assemblies of this type.
Conventionally, electrical assemblies such as power supply units in phone chargers, laptop computer adapters, or similar low-power applications are enclosed in boxes that are composed of plastic injection parts made from thermoplastic materials such as acrylonitrile butadiene styrene (ABS), polycarbonate (PC), or combinations thereof (PC+ABS). These are expensive materials, and structural considerations require that they be used in minimum thicknesses of 1.6 to 2.0 mm. Following assembly with the electronic components of the apparatus, such boxes are conventionally sealed by electronic welding or by a snap lock and screw.
Aside from the cost of the box itself, the above-described conventional boxes impose constraints 1) on the assembly process for sealing the box, particularly where extra parts such as screws are involved; 2) on the space available for the printed circuit board (PCB); on the method of securing the PCB assembly; and 3) on the size of the box.
In the mass production of small electrical assemblies such as phone chargers, laptop adapters, or other similar units, even a small reduction in size, design cost, or unit production cost can result in huge savings on millions of units. It is therefore highly desirable to provide a power supply box construction which reduces the material cost and facilitates assembly without compromising strength, insulation and safety.
The present invention overcomes the deficiencies of the prior art by providing a two-layer enclosure in which a two-part inner box injection-molded from 0.8 mm thick flame-retardant polybutylene terephthalate (PBT) houses the electronic components and one or more PCBs of the electrical assembly. The inner box is then assembled by simply overmolding it with a 1.0 mm thick flame-retardant polyvinyl chloride (PVC) layer which strengthens and protects the inner box and enhances its aesthetic appearance. The overmold also allows the customization of the unit for different plug variants, models or equipment manufacturers.
Substantial cost reductions are achieved due to the simplicity of the assembly and the use of thin-walled, low cost materials and cheaper tooling.